By Scott Nelson, On-Farm Network^® Director

This spring farmers will be pressed to accomplish a lot in a shortened season. However, by taking an extra 15 minutes to check the planter performance in the field could lead to a 15-bushel yield increase. 

Analysis of abundant research suggests a prudent goal is to achieve an even stand of 110,000 to 140,000 plants per acre. While farmers have been able to reach high soybean yields with lower final stands, abundant stands are more competitive with weeds. This drives the higher seeding recommendation by the Iowa Soybean Association’s (ISA) On-Farm Network®. 

Gaps in the soybean stand from poor seeding or uneven emergence costs farmers profit and contributes to poor weed control. Also, uneven emergence in soybeans cuts into profits as late emerging seedlings are crowded out by earlier emerging seeds, resulting in wasted seed. A newly published study¹ indicates that uneven emergence in soybeans cuts yields five to 10 percent, depending on the variety. 

Key areas to consider when seeding soybeans include planting depth, trench enclosure and stand gaps from drilling speeds. 

Planting depth

Like corn, soybeans are actually very sensitive to planting depth. Observations by the On-Farm Network team indicate that many soybean fields were planted at the wrong depth last year. The optimum depth for planting soybeans is 1 inch to 1.5 inches deep. If planting early or into moist soils, planting depth can be set to 1 inch. When planting later or under conditions such as dry soils or no-till, plant at a depth of 1.5 inches. 

In no-till production, if the planter is not equipped with residue cleaners, farmers should seed at the 1-inch depth to enable soybeans to push through the residue. Seeding soybeans at a half-inch can result in poor stands as physiological development of the seedling is hampered by shallow depth and not placed adequately into accessible moisture. If moisture is limiting, soybeans can be planted as deep as 2 inches, but this makes the stand vulnerable to crusting and soybean varieties with short hypocotyls may not emerge. 

Trench closure and sidewall compaction

Optimizing trench closure is also very important in achieving optimum stands in soybeans, especially in soils high in clay content. One of the worst situations in soybean production is when the seed trench opens after planting, exposing the seeds to drying and pre-emergence herbicides. If seed trench opening has been an issue in the past, farmers will want to investigate other styles of closing wheels. By fine tuning or modifying the closing wheels, significant stand improvement could be achieved.

Stand gaps

Drills, including modern high-speed drills, can be used profitably in soybean production. But operators must exercise caution as stand gaps can occur if the planting is not managed properly. 

In the photo below, several planting issues have become apparent. Seeding depth on the drill was set to 1 inch. Due to inadequate downforce pressure the seeding depth on the wings of the planter ranged from a half-inch to just beneath the residue. This allowed for stand gaps, increased weed pressure and ultimately lost profit. 

¹ “Spatial and temporal plant-to-plant variability effects on soybean yield.” European Journal of Agronomy 98 (2018) 14-24.

Source: Iowa Soybean Association

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